Otago study re-piecing prehistoric global warming

We think of climate change as a threat poised to heat our atmosphere, push up sea levels and acidify our oceans, making extreme weather a new norm.

But most of us would be less aware of the potentially critical implications of disturbing the long-term cycle of carbon through our atmosphere, through what scientists call negative feedback mechanisms.

A new study led by Associate Professor Claudine Stirling, of Otago University’s Research Centre for Oceanography, will investigate what these man-made disruptions to the planet’s climate might mean for its future.

The Earth was now in the midst of a “climate crisis”, Stirling said, with a carbon cycle disturbance comparable to those that drove biological turnover, and even mass-extinction events, in geological history.

“The side-effects of warmer global temperatures are already occurring, including ocean acidification, toxic phytoplankton blooms, and expansions of oxygen deprived conditions in the oceans,” she said.

“It is less well known that these threats are also negative feedback mechanisms that remove carbon from the atmosphere, and eventually re-stabilise the climate on geological timescales.”

The climate recovery process, however, was poorly constrained, and it was not known exactly when – or how – the natural climate system might return to “normal”.

It was even possible that our activity could have delayed the next natural glaciation cycle.

Stirling’s study, supported with a $960,000 Marsden Fund grant, will use bio-geochemical modelling and other approaches to step back millions of years into the planet’s history, to reveal the role of negative feedback during past global warming events.

These would be applied to a series of events that represented a range of CO2 emission scenarios, analogous to those we may face in the future.

“We will constrain the feedback mechanisms of the climate system to better understand the lifespan of human-induced climate change, providing crucial boundary conditions for modelling future climate scenarios.”

But doing so would require Stirling and her colleagues to understand each of the individual carbon removal processes involved.

“Such a systematic separation of parallel mechanisms has not yet been attempted in previous past-climate studies.”

Geochemical compositions of sediments that were formed continuously during different global warming episodes offered a wealth of information, as the secrets held in trace elements like iron, zinc, cadmium and uranium could tell scientists much about past climates.

The study would draw on one particular period in the Earth’s history – the early Cenozoic, between 44 and 58 million years ago, which saw a range of different global warming events often used to work out what could happen in the future.

By analysing sediments deposited throughout the period at sites around the world, the team will attempt to systematically tease out the action of each individual carbon removal process through the different events.

This would not only reveal the roles played by each of them, but also create a rich overall picture to inform climate models.

Stirling said New Zealand’s climate was closely inter-connected with global climate patterns.

“We have already observed some of the consequences of global warming, including, but not limited to, increasingly acidic oceans, and more frequent extreme weather events, including severe droughts and flooding in New Zealand.

“Gaining new insight regarding how climate recovery is likely to occur will be important for informing policy makers in New Zealand, and will assist them in making sound and informed decisions for the wellbeing of future generations.”

Otago Daily Times, 1 January 2018. Article.

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